Electronic Supplementary InformationFangxing Xiao* Research Institute of Photocatalysis, State Key...

Electronic Supplementary Information

A Novel Route for Self-Assembly of Gold Nanoparticles-TiO2

Nanotube Arrays (Au/TNTs) Heterostructure for Versatile

Catalytic Applications: Pinpoint Position via Hierarchically

Dendritic Ligand

Fangxing Xiao*

Research Institute of Photocatalysis, State Key Laboratory Breeding Base of

Photocatalysis, College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou

350002, P. R. China.

*To whom correspondence should be addressed.

E-mail Address: [email protected]

Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 2012

1. Experimental

1.1 Preparation of DTDTPA ligand

Dithiolated diethylentriaminepentaacetic (DTDTPA) and Au@DTDTPA nanoparticles (NPs)

were synthesized according to the Debouttiere’s method.1 - 3

In brief, 2 g of

diethylenetriaminepentacetic acid bis-anhydride (DTPA) was dissolved in DMF (40 mL) and

heated to 70 oC in a 250 mL round flask. In another flask, 1.1 g of aminoethanethiol was

dissolved in a mixed solution consisting of DMF (30 mL) and triethylamine (1.74 mL). This

solution was added to the round flask and stirred magnetically (2000 rpm) at 70 oC for 12 h.

Subsequently, the solution was cooled to room temperature and put in an ice bath. A white

powder precipitated was filtered and the acquired filtrate was concentrated at low pressure. White

precipitate was collected by adding the concentrated solution into a chloroform solution. After

filtration of the mixed solution, washed with 50 mL of chloroform, and dried under vacuum,

DTDTPA was obtained as white power.

1.2 Preparation of Au@DTDTPA and Au@Citrate

All the glasswares used were cleaned thoroughly with aqua regia (3 parts HCl, 1 part HNO3) for

12 h and rinsed completely with ddH2O. 200 mg of HAuCl4.4H2O in 70 mL of methanol was

mixed with a solution composing of 482 mg of DTDTPA, 50 mL of methanol, and 2 mL of acetic

acid, and stirred magnetically (2000 rpm) for 1 h. Then a freshly prepared solution of 192 mg

(NaBH4) was added under vigorous stirring (2500 rpm) for another 1 h. The color of the mixture

changed instantly from yellow to dark brown indicating the presence of Au NPs. The solution

was filtered through nylon membrane (0.2 µm) and washed with 100 mL of 0.01 N HCl, water,

diethyl ether, respectively, to obtain the Au@DTDTPA.

Au@Citrate was prepared by the Dotzauer’s method.4 Briefly, in a 100 mL Erlenmeyer flask,

25 mL of aqueous HAuCl4· 3H2O (1mM) solution was heated to a rolling boil under vigorous

stirring (2500 rpm). 2.5 mL of 38.8 mM aqueous sodium citrate was also heated to a rolling boil

and added rapidly to the above gold precursor solution. After 20 s, the mixture became dark and

then burgundy, heating was continued with vigorous stirring for 10 min, and finally the mixture

was stirred without heating for an additional 15 min to fulfill the synthesis. The as-prepared Au

NPs were stored in a refrigerator at 4 oC in a dark area and used within two weeks.

1.3 Electrochemical anodization preparation of TNTs

Titanium sheets (50 mm×20 mm×0.1 mm, 99.9 %, Xin RuiGe. Co. Beijing) were polished by

abrasive paper and ultrasonically washed by acetone, ethanol, and ddH2O for 15 min, respectively.

Afterward, titanium sheets were immersed into a mixed solution of HF-HNO3-H2O with volume

ratio of 1: 4: 5 for 30 s, washed by ddH2O and dried in a N2 stream. Anodization of Ti foil

was conducted in an organic electrolyte of ethylene glycol containing 0.5 % (w/v) NH4F and 2 %

(v/v) H2O, where the titanium sheet was used as a working electrode with a graphite sheet as a

counter electrode. The anodization of titanium foil was firstly carried out at 20 V for 2 h. After

which, the thus obtained samples were washed by ddH2O, dried in a N2 stream, and subsequently

sonicated for 5 min to remove the surface layer, the second anodization was subsequently carried

out under the same experimental conditions. Finally, the TNTs samples were gently sonicated and

annealed at 450 oC in air for 3 h to transform the amorphous phase of TiO2 to the anatase phase.


1.4 Self-assembly of the Au/TNTs heterostructure

TNTs (30 mm×10 mm×0.1 mm) was first vertically exposed to UV light (λ = 365 ± 15 nm) for

4 h to facilitate hydroxylation of the TiO2 surface,5-8

which could promote chemical bonding with

3-aminopropyl-trimethoxysilane (APS). TNTs were subsequently immersed in ethanol (50 mL)

by gentle ultrasonication for 1 h, and 500 μL of APS was added and refluxed for 4 h. The

APS-treated TNTs were sufficiently rinsed with ethanol to wash away residual APS and dried by

a N2 flow. 20 mg of Au@DTDTPA was dissolved in 10 mL of deionized water and sonicated for

10 min to attain a Au@DTDTPA aqueous solution of 2 g L-1

, the pH of which was carefully

mediated by 1 N NaOH at pH value of 6. The APS-treated positive charged TNTs was

immediately immersed in the negative charged Au@DTDTPA solution (2.5 mL, 2 g L-1

, pH = 6)

in a quartz cuvette with gentle stirring (200 rpm). After mixing for 1 h, the obtained mixture was

washed by deionized water (20 mL) for three times to remove any remaining Au@DTDTPA

solution and dried at 80 oC under vacuum for 12 h, thus giving rise to the Au@DTDTPA/TNTs

hybrid heterostructure. Subsequently, calcination at 300 oC for 4 h in O2 atmosphere to remove

organic component was performed to obtain the Au/TNTs heterostructure. 1, 9

For comparison, in

order to highlight the significant role of APS, the same experiments without using APS were also

carried out under analogous conditions.

1.5 Characterization

The phase composition of the sample was determined by X-ray diffraction (XRD) on a Bruker

D8 Advance X-ray diffractometer with Cu Kα radiation. The accelerating voltage and applied

current were 40 kV and 40 mA, respectively. Transmission electron microscopy (TEM),

energy-dispersive X-ray spectrometer (EDX), and high-resolution transmission electron

microscopy (HRTEM) images were obtained by a JEOL model JEM 2010 EX instrument at an

accelerating voltage of 200 kV. The UV-vis diffuse reflectance spectra (DRS) were recorded on a

Varian Cary 500 Scan UV-vis-NIR spectrometer, in which BaSO4 was used as the background

between the 200 nm and 800 nm regime. X-ray photoelectron spectroscopy (XPS) measurements

were conducted on an ESCALAB 250 photoelectron spectrometer (Thermo Fisher Scientific) at

2.4×10-10

mbar using a monochromatic Al Kα X-ray beam (1486.60 eV). Binding energy (BE)

of the element was calibrated to the carbon BE of 284.60 eV. The morphologies of the samples

were measured by field emission scanning electron microscopy (FESEM/EDX, FEI Nova

NanoSEM 230).

1.6 Photocatalytic activity

Photocatalytic activities of the samples were evaluated by using methyl orange (MO) as a model

organic dye pollutant compound. In a typical test, TNTs, Au@DTDTPA/TNTs, or Au/TNTs

sample with the same area of 3 cm2 was soaked into 3 mL of MO solution (5 mg/L) at pH value

of 7 in a quartz cuvette. Before irradiation, the mixtures were kept in the dark for 1 h to reach the

equilibrium of adsorption-desorption at room temperature. A 300 W Xe arc lamp (PLS-SXE

300C) equipped with a cutoff filter (λ = 365 ± 15 nm) was applied as the UV light source. The

temperature of the reaction system was controlled to be around 25 oC by a commercial electric

fan at ambient conditions. The irradiation time ranged from 5 min to 2.5 h. All the samples in the

quartz cuvette were placed ca. 21 cm away from the UV source with the same light intensity of

ca. 5 mW/cm2. At each time interval of 30 min, light absorption of the reaction solution was

measured by a Cary 500 scan UV-Vis spectrophotometer. The concentration of MO was

determined by the absorption of MO at 464 nm. The degradation ratio of MO at each time


interval was calculated from the difference of the light absorbance of irradiated to the

non-irradiated solution.

1.7 Photoelectrochemical measurement

Photoelectrochemical measurements were performed on a CHI 600D electrochemical system

(Chenhua Instruments Co. Shanghai). The system consisted of three electrodes, a

single-compartment quartz cell, which was filled with 0.1 M Na2SO4 electrolyte (30 mL), and a

potentiostat. A platinum black sheet was used as a counter electrode with Hg/Hg2Cl2/KCl as a

reference electrode. A thin film of TNTs or Au/TNTs (30 mm×10 mm) with impregnated area of

3 cm2 was employed as a working electrode. A 300 W Xe arc lamp (PLS-SXE 300C) equipped

with a band-pass light filter (λ = 365 ± 15 nm) was used as the exciting light source for UV light

irradiation. The intensity of light was controlled to be around 5 mW/cm2.

1.8 Catalytic reduction activity

In a typical reaction, blank TNTs, Au@DTDTPA/TNTs, or Au/TNTs sample (30 mm×10 mm×

0.1 mm) with an area of 3 cm2 was dipped into a mixed aqueous solution in a quartz cuvette

consisting of 2 mM (40 µL) 4-nitrophenol, 100 mM (400 µL) NaBH4, and 2 mL of ddH2O.

Afterward, the mixture was stirred (200 rpm) at room temperature for 30 min to generate uniform

aqueous solution. The use of a high excess of NaBH4 ensure that its concentration remains

essentially constant during the whole reaction, which allows the assumption of pseudo-first-order

kinetics with respect to the nitro compound. Samples of the reaction mixture were collected at

specific time interval (10 min) for UV-vis spectroscopy analysis. The light absorbance of the

characteristic peak of 4-nitrophenol at 400 nm was monitored.

2.0 2.5 3.0 3.50

5

10

15

20

25

30

Fre

qu

en

cy

(%

)

Diameter (nm)

Mean diameter= 2.82 ± 1.12 nm

Fig. S1 TEM image and mean diameter histogram of the Au@DTDTPA.

20 nm


OH

N

OHN

OH

N

NHS

NH

S

OHN

O

N

O

HON NH

S

NH

O

S

OO

O

O

O

O

O

OH

N

OH

N

OHN NH

S

NHS

OH

N

O

OH

N

O

HO

N

NH S

NH

O

SO

O

O

O

O

O

O

GNP

OH

Fig. S2 Chemical structure of DTDTPA profile and Au@DTDTPA.

DTDTPA

DTDTPA


Fig. S3 TEM images of Au/TNTs directly assembled of Au@DTDTPA to the TNTs framework

without APS.

Fig. S4 Schematic view of the self-assembly of Au NPs on the framework of TNTs.

Fig. S5 HRTEM image of single Au NP without the interference of TNTs.

50 nm 50 nm

5 nm 5 nm


Fig. S6 EDX patterns of (a) TNTs and (b) Au/TNTs heterostructure obtained from the SEM

measurement.

700 600 500 400 300 200 100 0

290 288 286 284 282 534 532 530 528

468 464 460 456 88 86 84 82

d

c

b

Binding Energy (eV)

Au4d Au4fC1sO1s

Ti2p

Binding Energy (eV)

a

eC 1s

Au 4fTi 2p

O 1s

f

g

Inte

nsit

y (

a.u

.)

Fig. S7 Survey XPS spectra of (a) Au@DTDTPA, (b) TNTs, (c) Au@DTDTPA/TNTs

heterostructure, and high-resolution spectra of (d) C 1s, (e) O 1s, (f) Ti 2p, and (g) A u 4f of the

Au@DTDTPA/TNTs heterostructure.

a b


Table S1. Chemical bond species versus binding energy for TNTs and Au@DTDTPA/TNTs

heterostructure.

Element TNTs (eV) Au@DTDTPA/TNTs (eV) Chemical Bond Species

C 1s A 284.62 284.60 C-C/C-H

C 1s B 286.18 286.21 C-OH/C-O-C

C 1s C 288.56 289.00 Carboxylate (CO3 2-

)

O 1s A 529.84 529.90 Lattice oxygen

O 1s B 531.40 531.04 Ti-OH

O 1s C 532.30 531.83 C-OH/C-O-C

O 1s D --- 533.07 COOH

Ti 2p3/2 458. 56 458.65 Anatase (4+)

Ti 2p1/2 464.25 464.47

Au 4f7/2 ---- 83.96 Au (0)

Fig. S8 TEM images of the Au@Citrate/TNTs nanostructure.

100 nm 20 nm


200 300 400 500 600 700

4

8

12

16

F(R

)

Wavelength (nm)

Au/TNTs

TNTs

Fig. S9 UV-vis diffuse reflectance spectra (DRS) of TNTs and Au@DTDTPA/TNTs

heterostructure.

3500 3000 2500 2000 1500 1000

O-H

Tra

nsm

itta

nce (

%)

Wavenumber (cm-1)

TNTs

Au@DTDTPA/TNTs

C=ON-H & O-H

O-H

C-H

Ti-OO-H

Fig. S10 FTIR results of TNTs and Au@DTDTPA/TNTs heterostructure.


20 25 30 35 40 45 50 55 60 65 70 75

c

b

Au (220)

Au (111)

Au (200)

A (211)

A (200)A (004)A (204)

T(103)T(102)

T(101)

Inte

ns

ity

(a

.u.)

2 Theta (Degree)

A (101)

T(002)

A-Anatase

T-Titanium

a

43 44 45 46

Inte

ns

ity

(a

.u.)

2 Theta (Degree)

Au (200)d

Fig. S11 XRD patterns of TNTs (a) before and (b) after heat treatment at 450 oC in air for 3 h, (c)

Au/TNTs heterostructure, and (d) magnified diffraction peak of Au (200) marked in c.


Fig. S12 Enlarged view of Fig. 2 in the manuscript for clear view.

References

1 F. X.. Xiao, F. C. Wang, X.. Z. Fu and Y. Zheng, J. Mater. Chem., 2012, 22, 7819.

2 F. X. Xiao, Y. Zheng, P. Cloutier, Y. H. He, D. Hunting and L. Sanche, Nanotechnology, 2011, 22, 465101.

3 P. J. Debouttiere, S. Roux, F. Vocanson, C. Billotey, O. Beuf, A. Favre-Reguillon, Y. Lin, S. Pellet-Rostaing,

R. Lamartine, P. Perriat and O. Tillement, Adv. Funct. Mater., 2006, 16, 2330.

4 D. M. Dotzauer, J. H. Dai, L. Sun and M. L. Bruening, Nano Lett. 2006, 6, 2268.

5 R. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kojima, A. Kitamura, M. Shimohigoshi and T.

Watanabe, Nature, 1997, 388, 431.

6 R. Wang, K. Hashimoto, A. Fujishima, M. Chikuni, E. Kojima, A. Kitamura, M. Shimohigoshi and T.

Watanabe, Adv. Mater., 1998, 10, 135.

7 R. Wang, N. Sakai, A. Fujishima, T. Watanabe and K. Hashimoto, J. Phys. Chem. B 1999, 103, 2188.

8 J. Zuo and E. Torres, Langmuir 2010, 26, 15161.

9 J. S. Lee, K. H. You and C. B. Park, Adv. Mater., 2012, 24, 1084.


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